Congestive heart failure remains a major public health problem, and is frequently the result of left ventricular remodeling after myocardial infarction. We have recently shown that human adult bone marrow contains endothelial progenitors with phenotypic and functional characteristics of embryonic hemangioblasts, and that these can be used to induce vasculogenesis after experimental myocardial infarction. This results in decreased apoptosis of hypertrophied myocytes, long- term salvage and survival of viable myocardium, reduction in collagen deposition, and sustained improvement in cardiac function. Thus, the use of cytokine-mobilized autologous human bone marrow-derived angioblasts offers the potential to significantly reduce morbidity and mortality associated with left ventricular remodeling. However, a number of studies have provided evidence that the ability of bone marrow-derived stem cells to respond to environmental demands such as injury, disease or other physiologic stimuli, may be compromised during aging. In the first part of this proposal we will investigate the relationship between increasing age or progression of ischemic heart disease and changes in the number, phenotypic characteristics, and in vitro and in vivo biologic properties of adult bone marrow-derived endothelial progenitors, or angioblasts. For these studies, 32 patients selected on the basis of incremental increase in age, and with a history of myocardial infarction (within previous 6-12 months with no evidence of heart failure, or greater than 5 years earlier and with heart failure), will be studied cross-sectionally and longitudinally. Phenotypic studies will be performed by flow cytometry of human bone marrow-derived cells obtained by leukapheresis after G-CSF mobilization. In vivo functional studies will involve intravenous injection of human angioblasts into athymic nude rats with experimental myocardial infarction. In the second part of this proposal we will seek to develop complementary strategies to augment the effects of angioblast- dependent vasculogenesis on cardiac function. We will first investigate whether angioblast migration to the infarct bed is regulated by chemokine-dependent interactions. We will then seek to increase angioblast trafficking to the heart and subsequent vasculogenesis by manipulating such interactions through use of monoclonal antibodies against chemokine receptors and induction of chemokine expression in the heart. Additional aims will be to evaluate whether the improvement in myocardial function obtained following angioblast-dependent vasculogenesis involves induction of myocyte proliferation/regeneration, and whether concomitant use of autologous mesenchymal stem cells or pharmacologic agents may provide synergistic, additive benefit. We believe that gaining an understanding of these issues will prove to be of critical importance in order to be able to rationally design and develop strategies for human clinical trials using autologous bone marrow-derived endothelial progenitors in the treatment of acute and chronic heart disease.